Fast epitaxial growth of a-axis- and c-axis-oriented YBa2Cu3O7−δ films on (1 0 0) LaAlO3 substrate by laser chemical vapor deposition

a-axis- and c-axis-oriented YBa₂Cu₃O_7−δ (YBCO) films were epitaxially grown on (1 0 0) LaAlO₃ substrates by laser chemical vapor deposition. The preferred orientation in the YBCO film changed from the a-axis to the c-axis with increasing laser powers from 77 to 158 W (the deposition temperatures from 951 to 1087 K). The a-axis-oriented YBCO film showed in-plane epitaxial growth of YBCO [0 0 1]//LAO [0 0 1], and the c-axis-oriented YBCO film showed that of YBCO [0 1 0]//LAO [0 0 1]. A c-axis-oriented YBCO film with a high critical temperature of 90 K was prepared at a deposition rate of 90 μm h⁻¹, about 2-1000 times higher than that of metalorganic chemical vapor deposition.     

Effect of oxygen pressure on microstructure and magnetic properties of strontium hexaferrite (SrFe12O19) film prepared by pulsed laser deposition

The effects of oxygen pressure during deposition on microstructure and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films grown on Si (100) substrate with Pt (111) underlayer by pulsed laser deposition have been investigated. X-ray diffraction pattern confirms that the films have c-axis perpendicular orientation. The c-axis dispersion (Δθ₅₀) increases and c-axis lattice parameter decreases with increasing oxygen pressure. The films have hexagonal shape grains with diameter of 150-250 nm as determined by atomic force microscopy. The coercivities in perpendicular direction are higher than those in in-plane direction, which shows the films have perpendicular magnetic anisotropy. The saturation magnetization and anisotropy field for the film deposited in oxygen pressure of 0.13 mbar are comparable to those of the bulk strontium hexaferrite. Higher oxygen pressure leads to the films having higher coercivity and squareness. The coercivity in perpendicular and in-plane directions of the film deposited in oxygen pressure of 0.13 mbar are 2520 Oe and 870 Oe, respectively.     

Influence of the crystal orientation on the electrical properties of AlN thin films on LTCC substrates

In this study, the influence of the crystal orientation on the electrical properties of sputter deposited aluminium nitride (AlN) thin films on low temperature co-fired ceramics (LTCC) substrates is investigated. The degree of c-axis orientation can be tailored by the deposition conditions such as plasma power, gas pressure and gas composition in the deposition chamber. Due to the large surface roughness of LTCC substrates (R_a = ∼0.4 μm) the quality of thin films is lower compared to silicon. Between areas of columnar grains arranged perpendicular to the LTCC surface, defects like voids are generated due to the wavy surface characteristics. The impact of crystal orientation and temperature up to 400 °C on the electrical performance is evaluated, as these layers are targeted as potential candidates for dielectric heat spreaders on multilayered ceramic substrates for high frequency applications. These AlN thin films having a good c-axis orientation exhibit lower leakage current levels over the complete temperature range compared to those with a poor alignment with respect to this crystallographic plane. The leakage current behaviour, however, is dominated according to the Pool-Frenkel electron emission independent of the degree of c-axis orientation.     

Enhanced ferroelectric properties of vanadium doped bismuth titanate (BTV) thin films grown by pulsed laser ablation technique

Bi_3.99Ti_2.97V_0.03O₁₂ (BTV) thin films were grown by pulsed laser deposition at substrate temperatures ranging between 650 and 750 °C. The structural phase, and orientation of the deposited films were investigated in order to understand the effect of the deposition parameters on the properties of the BTV films. As the substrate temperature was increased to 700 °C, the films started showing a tendency of assuming a c-axis preferred orientation, while at lower temperatures polycrystalline films were formed. The Au/BTV/Pt capacitor showed an interesting dependence of the remnant polarization (P_r) as well as dc leakage current values on the growth temperature. The film deposited at 675 °C showed a very large 2P_r of 42 μC cm⁻², which is the largest for BTV thin films among the values reported so far.     

Characteristics of filtered vacuum arc deposited ZnO-SnO2 thin films on room temperature substrates

ZnO, SnO₂ and zinc stannate thin films were deposited using filtered vacuum arc deposition (FVAD) system on commercial microscope glass and UV fused silica substrates (UVFS) at room temperature (RT). The structural and morphological analyses were performed using X-ray diffraction (XRD) and Atomic Force Microscopy (AFM), respectively. XRD patterns of ZnO films deposited at RT had strongly c-axis orientation, whereas SnO₂ and zinc stannate films had amorphous structure as they did not have any defined patterns. Average crystalline size and surface grain size of ZnO films were ∼16 nm, as determined from diffraction line broadening and AFM images, respectively. Optical constants in the 250-1100 nm wavelength range were determined by variable angle spectroscopic ellipsometry and transmission measurements. The transmission of the deposited films in the VIS was 80-90%, affected by interference. The refractive indices and the extinction coefficients of deposited ZnO, SnO₂ and zinc stannate films were in the range 1.87-2.15 and 0.02-0.04, depending on wavelengths and deposition parameters. The optical band gap (E_g) was determined by the dependence of the absorption coefficient on the photon energy at short wavelengths. Its values for ZnO, SnO₂ and zinc stannate were in the range 3.25-3.30 eV, 3.60-3.98 eV and 3.43-3.52 eV, respectively, depending on the deposition pressure.     

Influence of the deposition pressure on the properties of transparent conducting zirconium-doped zinc oxide films prepared by RF magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films with high transparency and relatively low resistivity have been successfully prepared by RF magnetron sputtering at room temperature. The deposition pressure was varied from 0.6 to 2.5 Pa. A transformation from a relatively compact structure to individual grains was observed with the increase of deposition pressure. As the deposition pressure increases, the resistivity increases sharply due to both, the decrease of hall mobility and carrier concentration. The lowest resistivity achieved was 2.07 × 10⁻³ Ω cm at a deposition pressure of 0.6 Pa with a hall mobility of 16 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.95 × 10²⁰ cm⁻³. The films are polycrystalline with a hexagonal structure and a preferred orientation along the c-axis. All the films present a high transmittance of above 90% in the visible range. The optical band gap decreases from 3.35 to 3.20 eV as the deposition pressure increases from 0.6 to 2.5 Pa.     

The crystalline orientation and ferroelectric properties of Bi3.25La0.75Ti3O12 thin films mediated by the intermediate layer of LaNiO3

c-Axis-oriented and (1 1 7)-oriented Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films are successfully controlled by the intermediate layer of LaNiO₃ (LNO) with chemical solution deposition (CSD), respectively. X-ray diffraction (XRD) demonstrates that the structure and orientation of LNO thin films have a strong effect on the orientation of BLT thin films. Scanning electron microscopy suggests that BLT thin films on LNO electrode exhibit crack-free, uniform size grains and dense microstructure. A crystalline orientation dependent remanent polarization is observed in BLT thin films, and it is found that the remanent polarization (2P_r) of (1 1 7)-oriented films is larger than that of c-axis-oriented films. Our research directly demonstrates that the vector of the main spontaneous polarization in these layered perovskite materials (BLT) is along a-axis.     

Role of vanadium content in ZnO thin films grown by pulsed laser deposition

Vanadium-doped ZnO films (Zn_1−xV_xO, where x = 0.02, 0.03, 0.05 and 0.07), were formed from ceramic targets on c-cut sapphire substrates using pulsed laser deposition at substrate temperature of 600 °C and oxygen pressure of 10 Pa. In order to clarify how the vanadium concentration influences the films’ properties, structural and magnetic investigations were performed. All films crystallised in wurtzite phase and presented a c-axis preferred orientation at low concentrations of vanadium. The results implied that the doping concentration and crystalline microstructure influence strongly the system's magnetic characteristics. Weak ferromagnetism was registered for the film with the lowest doping concentration (2 at.%), which exhibited a ferromagnetic behavior at Curie temperature higher than 300 K. Increasing the vanadium content in the film caused degradation of the magnetic ordering.     

Magnetic properties of strontium hexaferrite films prepared by pulsed laser deposition

The magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films fabricated by pulsed laser deposition on the Si(100) substrate with Pt(111) underlayer have been studied as a function of film thickness (50–700 nm). X-ray diffraction patterns confirm that the films have c-axis perpendicular orientation. The coercivities in perpendicular direction are higher than those for in-plane direction which indicates the films have perpendicular magnetic anisotropy. The coercivity was found to decrease with increasing of thickness, due to the increasing of the grain size and relaxation in lattice strain. The 200 nm thick film exhibits hexagonal shape grains of 150 nm and optimum magnetic properties of M_s=298 emu/cm³ and H_c=2540 Oe.     

Structural, magnetic and electric properties of HoMnO3 films on SrTiO3(001)

HoMnO₃ films were grown on pure and Nb-doped SrTiO₃ (001) substrates by pulsed laser deposition. The films grew epitaxially with the c-axis along the substrate normal. Varying the deposition temperature between 650 and 850 °C did not significantly affect the structural and magnetic properties of the films, whereas growth in oxygen partial pressures below 0.01 mbar lead to a degradation of the structural properties. Some of the films had a ferromagnetic-like magnetic phase transition at about 45 K, probably related to Mn₃O₄ precipitates; this magnetic response was isotropic. The Ho sublattice was found to be paramagnetic down to 5 K, but showing a pronounced anisotropy with the c-axis being the hard axis. The films showed a distinct dielectric anomaly at 16 K that depended on voltage and slightly on frequency in the range between 1 kHz and 1 MHz. The magnetoelectric effect was large with an in-plane field of 8 T suppressing the dielectric anomaly completely.     

Structural, morphological and photoluminescence properties of W-doped ZnO nanostructures

W-doped ZnO nanostructures were synthesized at substrate temperature of 600 °C by pulsed laser deposition (PLD), from different wt% of WO₃ and ZnO mixed together. The resulting nanostructures have been characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and photoluminescence for structural, surface morphology and optical properties as function of W-doping. XRD results show that the films have preferred orientation along a c-axis (0 0 L) plane. We have observed nanorods on all samples, except that W-doped samples show perfectly aligned nanorods. The nanorods exhibit near-band-edge (NBE) ultraviolet (UV) and violet emissions with strong deep-level blue emissions and green emissions at room temperature.     

On the use of response surface methodology to predict and interpret the preferred c-axis orientation of sputtered AlN thin films

This paper deals with experimental design applied to response surface methodology (RSM) in order to determine the influence of the discharge conditions on preferred c-axis orientation of sputtered AlN thin films. The thin films have been deposited by DC reactive magnetron sputtering on Si (1 0 0) substrates. The preferred orientation was evaluated using a conventional Bragg-Brentano X-ray diffractometer (θ-2θ) with the CuKα radiation. We have first determined the experimental domain for 3 parameters: sputtering pressure (2-6 mTorr), discharge current (312-438 mA) and nitrogen percentage (17-33%). For the setup of the experimental design we have used a three factors Doehlert matrix which allows the use of the statistical response surface methodology (RSM) in a spherical domain. A four dimensional surface response, which represents the (0 0 0 2) peak height as a function of sputtering pressure, discharge current and nitrogen percentage, was obtained. It has been found that the main interaction affecting the preferential c-axis orientation was the pressure-nitrogen percentage interaction. It has been proved that a Box-Cox transformation is a very useful method to interpret and discuss the experimental results and leads to predictions in good agreement with experiments.     

Structure and optical properties of nanostructured zinc oxide films with different growth temperatures

ZnO films were prepared by pulsed laser deposition (PLD) on glass substrate with temperature ranging from room temperature (RT) to 500 °C. All the films formed the hexagonal wurtzite structure and showed the c-axis (0 0 2) preferred orientation. The films deposited at 200 °C showed the narrowest full width at half maximum of both X-ray diffraction (XRD) and rocking curve, largest height grain size, smallest macrostress and least point defects. Meanwhile, it was found that the films deposited at 350 °C displayed the most intense diffraction peak in XRD and a strong UV emission while it showed the most intense defect-related green emission, fastest growth rate and larger macrostress. In addition, the cross section images showed all films grew with a columnar form along (0 0 2) orientation.     

Optical properties of ZnO and ZnO:Ce layers grown by spray pyrolysis

In this paper, zinc oxide (ZnO) and cerium-doped zinc oxide (ZnO:Ce) films were deposited by reactive chemical pulverization spray pyrolysis technique using zinc and cerium chlorides as precursors. The effects of Ce concentration on the structural and optical properties of ZnO thin films were investigated in detail. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) measurements. All deposited ZnO layers at the temperature 450 °C are polycrystalline and indicate highly c-axis oriented structure. The dimension of crystallites depends on incorporation of Ce atoms into the ZnO films. The photoluminescence spectra of the films have been studied as a function of the deposition parameters such as doping concentrations and post grows annealing. Photoluminescence spectra were measured at the temperature range from 13 K to 320 K.     

Influence of Hf doping concentration on microstructure and optical properties of HfxZn1−xO thin films

Hf_xZn_1−xO thin films (x=3, 7, 10 and 15 mol%) were deposited on Si (1 0 0) using pulsed laser deposition. The influence of the Hf concentration on the microstructure and optical properties of the films was studied. It is found that Hf ions can be effectively doped into ZnO and all films crystallize in the hexagonal wurtzite structure with a preferred c-axis orientation. The lattice constants of Hf_xZn_1−xO films increase with the Hf contents. Two ultraviolet peaks centered at about 364 and 380 nm coexist in the fluorescent spectra. With increasing the Hf contents, the intensity of fluorescent peaks enhances remarkably. At the same time the energy gaps gradually increase, while the positions of ultraviolet peaks remain unchanged. The mechanism of luminescent emission for Hf_xZn_1−xO films was discussed.     

Potential of Nd:YAG pulsed laser deposition method for coated conductor production

A Nd:YAG laser is environmentally safe and economical with no poisonous or hazardous gases and no expensive gases. We prepared Y123 films by using the fourth harmonic Nd:YAG pulsed laser deposition (PLD) method and optimized the deposition conditions on MgO single crystalline substrates and IBAD-MgO substrates for Y123 coated conductor. We found that the optimal deposition conditions acquired bi-axially aligned Y123 films on both substrates with T_c ∼ 90 K and J_c > 1 MA/cm² at 77 K in self-field. For obtaining high I_c, we fabricated thick Y123 films on both substrates and the maximum I_c per 1 cm in width reached 186 A/cm-width on the IBAD-MgO substrate. Interestingly, there were no a-axis oriented grains within the films up to 1.8 μm thick. This might be an especial feature of the Nd:YAG-PLD method. We believe that the Nd:YAG-PLD method is promising method for RE123 coated conductor production.     

Structural and optical properties of nano-structured tungsten-doped ZnO thin films grown by pulsed laser deposition

Novel highly c-oriented tungsten-doped zinc oxide (WZO) thin films with 1 wt% were grown by pulsed laser deposition (PLD) technique on corning 1737F glass substrate. The effects of laser energy on the structural, morphological as well as optical transmission properties of the films were studied. The films were highly transparent with average transmittance exceeding 87% in the wavelength region lying between 400 and 2500 nm. X-ray diffraction analysis (XRD) results indicated that the WZO films had c-axis preferred orientation with wurtzite structure. Film thickness and the full width at half maximum (FWHM) of the (0 0 2) peaks of the films were found to be dependent on laser fluence. The composition determined through Rutherford backscattering spectroscopy (RBS) appeared to be independent of the laser fluence. By assuming a direct band gap transition, the band gap values of 3.36, 3.34 and 3.31 eV were obtained for corresponding laser fluence of 1, 1.7 and 2.7 J cm⁻², respectively. Compared with the reported undoped ZnO band gap value of 3.37 eV, it is conjectured that the observed low band gap values obtained in this study may be attributable to tungsten incorporation in the films as well as the increase in laser fluence. The high transparency makes the films useful as optical windows while the high band gap values support the idea that the films could be good candidates for optoelectronic applications.     

Scanning tunnelling microscopy studies of growth morphology in highly epitaxial c-axis oriented Pt thin film on (0 0 1) SrTiO3

A noble metal Pt thin film was successfully grown on (0 0 1) SrTiO₃ substrate by using a DC-sputtering technique. The surface morphology and growth features of the as-grown Pt films were investigated by scanning tunnelling microscopy. Growth conditions, such as pre-sputtering, deposition ambience, and oxygen ratio are found to greatly affect the orientation, the crystallinity, and the epitaxial behavior of Pt films on (0 0 1) SrTiO₃. Single-crystalline Pt films have been achieved by introducing a few percentage oxygen into the sputtering ambient. The in-plane-relationship of the c-axis oriented Pt thin films on (0 0 1) SrTiO₃ was determined to be (0 0 1)_Pt∥(0 0 1)_SrTiO3 and [0 0 1]_Pt∥[0 0 1]_SrTiO3. Oxygen in the sputtering ambient was found to be a key factor to achieve the epitaxial Pt films.     

Structural and optical characterization of undoped, doped, and clustered ZnO thin films obtained by PLD for gas sensing applications

The synthesis by pulsed laser deposition technique of zinc oxide thin films suitable for gas sensing applications is herein reported. The ZnO targets were irradiated by an UV KrF^* (λ = 248 nm, τ_FWHM ∼7 ns) excimer laser source, operated at 2.8 J/cm² incident fluence value, whilst the substrates consisted of SiO₂(0 0 1) wafers heated at 150 °C during the thin films growth process. The experiments were performed in an oxygen dynamic pressure of 10 Pa. Structural and optical properties of the thin films were investigated. The obtained results have demonstrated that the films are c-axis oriented. Their average transmission in the visible-infrared spectral region was found to be about 85%. The equivalent refractive indexes and extinction coefficients were very close to those of the tabulated reference values. Doping with 0.5% Au and coating with 100 pulses of Au clusters caused but a very slight decrease (with a few percent) of both transmission and refractive index values. The coatings with the most appropriate optical properties as waveguides have been selected and their behavior was tested for butane sensing.     

Correlation between structural and mechanical properties of PbTiO3 thin films grown by pulsed-laser deposition

Tetragonal lead titanate (PbTiO₃, PT) thin films are grown on (1 0 0) MgO substrate by pulsed-laser deposition (PLD) for expected applications in integrated optics. The realisation of outstanding and reliable devices into integrated circuits requires sufficient mechanical resistance despite that the obtained PT films display interesting waveguiding properties associated with low optical losses. Two mechanical properties characteristic of elasticity and hardness of PT films are studied. The elastic modulus (E or Young's modulus) and the hardness (H) are measured by the nanoindentation technique. These mechanical properties are correlated to the crystalline quality of PT/MgO thin films. The films show epitaxial relationship with the MgO substrate and the orientation of crystallites perpendicularly to the surface substrate may be the consequence of a growth process along c-axis, a-axis or both. Differences on curves plotting hardness and elastic modulus as a function of indentation depth are observed as the curves are less dispersed for the films mainly c-axis oriented.